1. Field of the Invention
The present invention relates to an inkjet recording apparatus, and more particularly, to technology for repairing recording errors caused by ink discharge failures during image recording in an inkjet recording apparatus.
2. Description of the Related Art
An inkjet type image forming apparatus has an inkjet head (print head) in which a plurality of nozzles are arranged, and it forms images on a recording medium by discharging ink from the nozzles while moving the print head and the recording medium relatively with respect to each other.
In an inkjet recording apparatus of this kind, blocking of the nozzles of the print head or soiling of the ink meniscus may give rise to printing errors in which ink fails to be discharged or ink is not discharged in the correct direction of flight, thus leading to omissions in the print. Printing omissions of this kind are not readily noticeable in the case of a shuttle scan system, since there is a large degree of overlap in the print, but in the case of a line head, printing omissions are highly noticeable.
Therefore, various methods for detecting print omissions caused by discharge failure of this kind and methods for rectifying print omissions when they are detected, have been proposed.
In one known example, it is determined whether or not ink particles have been discharged correctly by comparing the printed dots with the print data, by means of an image sensor (see, for example, Japanese Patent Application Publication No. 63-260448).
In a further known example, a test pattern is recorded onto a recording medium, this test pattern is read out by a discharge failure detection device, and if it is determined that an ink discharge failure has occurred in a portion of the plurality of discharge ports, then the supply of drive data for discharging ink from the discharge ports is changed by means of discharge ports other than a discharge port which has produced a discharge failure. Thereby, even if a discharge failure has occurred in a portion of the discharge ports of the recording head, it is still possible to assign this drive data to other discharge ports which are functioning normally. Therefore, recording can even be performed by a recording head in which a portion of the nozzles have produced discharge failures (see, for example, Japanese Patent Application Publication No. 5-338199).
In a further known example, the image recording status recorded onto a special test recording member is read in by a reading device, and the driving the recording device is controlled on the basis of the image information thus read out. Furthermore, the image recorded onto the test recording member is erased so that the member can be reused (see, for example, Japanese Patent Application Publication No. 6-340063).
In yet a further known example, it is judged, on the basis of bit map data for a black ink recording head, whether or not there is a region where dots are to be formed by black ink in a line corresponding to those nozzle openings in a color (other than black) recording head that are required to perform at least dummy discharge. When the nozzle openings of the color ink recording head which are required to perform dummy discharge are positioned facing the positions at which dots of black ink are to be formed, the nozzle openings of the color ink recording head required to perform dummy discharge are caused to discharge ink droplets of one color onto one point, separately from the print data. Dots of black ink based on the print data are subsequently printed and superimposed onto the color dots formed by the dummy discharges, thereby concealing the color dots of the dummy discharges. Therefore, it is possible to avoid nozzle blockages by performing dummy discharges during printing, without having to interrupt the printing operation (see, for example, Japanese Patent Application Publication No. 9-216388).
However, in Japanese Patent Application Publication No. 63-260448, in the case of a single-pass system which does not involve overwriting, or a system using high-density nozzles or a high number of nozzles, the adjacently positioned dots overlap closely with each other, and therefore it is not possible to detect discharge failures accurately by detecting the dots.
Furthermore, in Japanese Patent Application Publication No. 5-338199, discharge failures are detected by recording a test pattern onto a recording medium, and therefore wasted recording medium is generated. In Japanese Patent Application Publication No. 6-340063, a special, separate recording medium for determination is required, and although this medium can be reused, a special cleaning device for the recording medium is also required in order that it can be reused. Therefore, the composition of the device becomes complicated.
In Japanese Patent Application Publication No. 9-216388, nozzle blockages are prevented by performing a dummy discharge during printing, but discharge failures are not detected and therefore countermeasures cannot be adopted during printing if a discharge failure has occurred. The printing operation must be interrupted in order to perform a restoring operation with respect to the nozzles.